There are many occasions when a mixture of particles of different types must be separated; for example in the recovery of ore and in the sorting of trash. The different magnetic properties of the materials may permit a separation to be accomplished by passing the particles through a magnetic field, but, when the materials are not magnetically attractive, other separation techniques are necessary. Many materials, particularly plastic materials are electrically neutral and are not affected by magnetic charging, and thus separation depending on magnetic effects is not feasible. Separation based on differences in specific gravities is also widely used where possible, but in the case of plastic materials the specific gravities of different materials are frequently too similar to form a basis for such separation. It has now been found that such electrically neutral materials may be given a temporary surface charge that is sufficiently strong and persistent to permit a separation based on the different charges received by different materials.
It is an object of this invention to provide a process and apparatus for separating mixtures of two or more types of particles of electrically neutral materials. It is another object of this invention to provide a process and an apparatus for subjecting a feed mixture of electrically neutral particles of synthetic plastic material to a series of directional changes and interparticle contacts while in turbulent flow to produce particles with temporary surface charges, and separating those particles based on their surface charges. Still other objects will become apparent from the more detailed description which follows.